One hundred and six female patients with symptomatic LSS who presented between January 2009 and December 2009 were enrolled in this study. The inclusion criteria were being postmenopausal, having walking difficulty due to neurogenic claudication caused by LSS, and a stenotic lesion in the lumbar spine confirmed by magnetic resonance imaging (MRI). We defined stenotic lesion as midsagittal diameter being smaller than 12 mm in MRI.11
The exclusion criteria were having a history of chronic systemic disease or peripheral vascular disease, showing evidence of metabolic bone diseases such as hypo- or hyperparathyroidism and chronic renal disease, or using bone-specific medications (hormone replacement, bisphosphonates, and corticosteroids), and having concurrent serious medical conditions affecting bone metabolism, including sepsis or neoplasia.
All patients were scheduled to be treated with lumbar spinal decompression and/or posterior spinal fusion. Patients’ demographic characteristics were obtained and each completed a questionnaire assessing for osteoporotic risk factors .12
Preoperative imaging studies included plain radiographs of the lumbar and thoracic spine, including dynamogram of designated level and both knee joints. MRI of the lumbosacral spine was performed to confirm LSS and subsequently plan lumbar spinal surgery was done. For the assessment of functional disability due to spinal stenosis, the Oswestry Disability Index (ODI) was recorded before the surgical treatment. Osteoporotic profiles included measurement of lumbar and hip bone mineral density (BMD) (Hologic, Waltham, MA, USA), serum vitamin D concentration, urinary-N-terminal telopeptide (u-NTx) as a bone resorption marker, and serum osteocalcin and serum alkaline phosphatase as bone formation markers.
Total lumbar (lumbar 2nd
), total hip, and femoral neck BMD were measured. The BMD of the Ward triangle was not counted in this study. Patients with a T score below –2.5 in at least one of the three sites were diagnosed with osteoporosis. Patients with a T score between –2.5 and –1.0 in at least one of the three sites were diagnosed with osteopenia. Patients with prevalent vertebral fractures and a T score below –2.5 were diagnosed with severe osteoporosis.13
OA of the knee and hip joint was graded using the Kellgren–Lawrence method.14
Patients with Kellgren–Lawrence grade II, III, and IV radiographic findings in the knee and hip joint were regarded as having OA.
u-NTx was measured from a morning urine sample using a chemiluminescent-based method (Ortho ECi, Ortho-Clinical Diagnostics, Raritan, NJ, USA). The coefficient of variation was 2.42%. Alkaline phosphatase was measured in a fasting early morning venous blood sample using an enzymatic method (Hitachi 7600, Hitachi Co., Tokyo, Japan). The coefficient of variation was 2.88%.
Osteocalcin was measured in a fasting morning blood sample by electrochemiluminescence immunoassay (ECLIA) (Modular E170, Roche Diagnostics, Mannheim, Germany). The coefficient of variation was 2.26%. 25-hydroxyvitamin D [25(OH)D] was measured by radioimmunoassay (DiaSorin Inc., Stillwater, OK, USA), and a serum vitamin D level below 20 ng/ml was classified as hypovitaminosis D. A seasonal correction was not made; however, all blood and urine specimens were collected in the morning to correct for diurnal variation.
The demographic data and disease-related variables such as ODI and symptom duration were analyzed by logistic regression analysis. Odds ratio for osteoporosis or osteopenia was evaluated by stepwise multivariate logistic regression with a forward stepwise procedure. All statistical analyses were performed using the SPSS 12.0.1 statistical package (SPSS, Inc., Chicago, IL, USA). A value of P<0.05 was accepted as significant.
Treatment guidelines for osteoporosis were defined as a subject having 1) a T score below –1.5 with positive risk factors for osteoporosis, 2) a T score below –2.0 without risk factors for osteoporosis, and 3) any fragility fractures as cited by the National Osteoporosis Foundation (NOF).15
These NOF-designated risk factors are: (1) history of adult fracture, (2) adult fracture in a first-degree relative, (3) current cigarette smoking, and (4) weight <58 kg.